Download Variance components and selection response for feather pecking

Archived at http://orgprints.org/1563
Genetic improvement on feather pecking behaviour by selection is promising
G. Su, J. B. Kjaer and P. Sørensen
Danish Institute of Agricultural Sciences, P.O. Box 39, Foulum, DK - 8830 Tjele, Denmark
Long term selection of laying hens for production in cage systems could have resulted in a poor
adaptation to other rearing systems. One of the problems with the poor adaptation is feather
pecking. The objective of the present study was to investigate genetic variation in feather pecking
behaviour and genetic improvement on this trait by selection using an appropriate datatransformation and an animal model.
Selection experiment In the selection experiment, line LP was selected for low feather pecking,
line HP for high feather pecking. At about 30 weeks of age, female feather pecking behaviour was
recorded for floor housed hens by video-camera for 3 hours (about 20 hens in each pen). Selection
was based on number of feather pecking bouts. In each generation 10 males (from about 50) and 30
females (from about 200) were selected as breeding birds in each line.
Statistical analysis The data for each line were analysed separately using an animal model:
yt = year-hatch + pen + full-sib group + additive genetic+ residual
where yt is the number of bouts of feather pecking in Box-Cox transformation scale, i.e.,

y t  ( y  1)
 , for   0,
y t  log( y ), for   0 , ( y>0)
where y is the number of bouts in original scale plus one (to meet y>0). A set of  ranging from -1
to 1 with interval 0.1 were used to do the transformation. The variance components and breeding
values were estimated basing on the transformation that gave the largest maximum likelihood.
Table 1. Phenotypic mean and standard deviation of bout
Results The transformation giving
number in observed scale and transformed scale
the largest maximum likelihood was
Line Gene- N
Bouts (obs.)
Bouts (trans.)
that with =-0.2 in both lines. A
ration
general statistic is shown in Table 1.
Mean Std
Mean Std
Bout number averaged over
LP
0
193 2.82
6.15 0.701 0.677
selection generations in line HP was
1-4
867 2.24
7.67 0.499 0.622
much higher than that in line LP.
HP
0
200 2.42
5.31 0.661 0.656
The coefficient of variation was
1-4
850 7.20
23.9 0.878 0.815
about 100% in transformed scale and
300% in observed scale.
Table 2. phenotypic variance (p2), ratio of variance for pen
effects (c2) and for full-sib group effects (f2), heritability (h2),
and total selection response (Rt).
Line p2
c2
f2
Rt
h2 SE
LP
0.3984 0.009 0.000 0.181  0.08 -0.433
HP
0.6313 0.007 0.000 0.154  0.07
0.555
Table 2 shows variance
components and selection
response for feather pecking in
transformed scale with =-0.2.
The ratio of variance for pen
effect and for full-sib group effect turned to zero. The estimates of heritability were similar to each
other. After 4 generations of selection the total response was 62% of base population mean in line
LP and 84% in line HP.
Conclusions
Large phenotypic variation for feather pecking behaviour.
No full-sib group effect can be found, indicating that maternal effect is negligible.
Moderate or low heritability.
Genetic improvement on feather pecking by selection is effective.